Some of Arnett's early days in journalism were in Southeast Asia, particularly Bangkok. He started out running a small English-language newspaper in Laos in 1960.[2] Eventually, he made his way to Vietnam where he was a reporter for the Associated Press. He worked with other AP staff in their Saigon office writing a number of important articles, such as "Death of Supply Column 21", which attracted the ire of the American government.[2] In July 1963, he was punched in the nose by South Vietnamese undercover police while covering Buddhist protests.

He went on dozens of missions with troops, including during the traumatic battle of Hill 875, in which a detachment went to try to rescue another unit of soldiers that was stranded in hostile territory. They themselves were nearly killed during the rescue. In September 1972 he accompanied a group of U.S. peace activists, including William Sloane Coffin and David Dellinger, to Hanoi, North Vietnam to bring three prisoners of war back to the United States.[citation needed]

Arnett got into trouble for writing in an unvarnished manner when trying to report the stories of ordinary soldiers and civilians. Arnett's writing often was perceived as negative. General William Westmoreland and president Lyndon B. Johnson and other people in power had battles with the AP over trying to get Arnett removed from his assignment.[citation needed]

Arnett's most famous act of reporting from the Vietnam War was a story published on 7 February 1968, about the provincial capital Bến Tre: "'It became necessary to destroy the town to save it,' a United States major said today. He was talking about the decision by allied commanders to bomb and shell the town regardless of civilian casualties, to rout the Vietcong."[3] The quotation was distorted in subsequent publications, eventually becoming the more familiar, "We had to destroy the village in order to save it."[4] The accuracy of the original quotation and its source have often been called into question. Arnett never revealed his source, except to say that it was one of four officers he interviewed that day.[4] US Army Major Phil Cannella, the senior officer present at Bến Tre, suggested that the quotation might have been a distortion of something he said to Arnett.[4]The New Republic at the time attributed the quotation to US Air Force Major Chester L. Brown.[5] In Walter Cronkite's 1971 book, Eye on the World, Arnett reasserted that the quotation was something "one American major said to me in a moment of revelation."[6]

Arnett was one of the last western reporters in Saigon after its capture by the North Vietnamese Army, and met with NVA soldiers who showed him how they had entered the city.[citation needed]

Following the Soviet Invasion of Afghanistan, Arnett was working for Parade and with a contact named Healy entered Afghanistan illegally from Pakistan, both dressed as natives and led by Mujahideen guides. They continued on to a Jalalabad hideaway of approximately fifty rebels. The trip came to an end when Healy fell into the Kunar River, ruining the pair's cameras. Later, Arnett would recount the story to Artyom Borovik who was covering the Soviet side of the war.[8]

Arnett worked for CNN for 18 years ending in 1999. During the Gulf War he became a household name worldwide when he became the only reporter with live coverage directly from Baghdad. His dramatic reports were often given with air raid sirens blaring and the sound of US bombs exploding on Baghdad in the background. Together with two other CNN journalists, Bernard Shaw and John Holliman, Arnett brought continuous coverage from Baghdad for the 16 initial intense hours of the war (17 January 1991). Although 40 foreign journalists were present at the Al-Rashid Hotel in Baghdad at the time, only CNN possessed the means -- a satellite phone -- to communicate to the outside world. CNN broadcast Arnett's extended call live for several hours, with a picture of Arnett as video. Soon the other journalists left Iraq, including the two CNN colleagues, which left Arnett as the sole reporter remaining there.

His reports on civilian damage caused by the bombing were not received well by the coalition war administration, who by their constant use of terms like "smart bombs" and "surgical precision" had tried to project an image that civilian casualties would be at a minimum. White House sources would later state that Arnett was being used as a tool for Iraqi disinformation and CNN received a letter from 34 Members of the United States Congress accusing Arnett of "unpatriotic journalism".

Two weeks into the war, Arnett was able to obtain an uncensored interview with Saddam Hussein.[9] The Gulf War became the first war to be seen truly live on TV, and Arnett was in many ways the sole player reporting from the "other side" for a period of five weeks.

About halfway through the war the CIA approached Mr. Arnett. They believed that the Iraqi military was operating a high-level communication network from the basement of the Al Rashid Hotel, which is where Mr. Arnett and a few others from CNN were staying. The CIA wanted him out so the Air Force could bomb the hotel, but Mr. Arnett refused. He said he had been given a tour of the hotel and denied there was such a facility.[10]

The report, titled The Valley of Death, claimed that the United States Army had used Sarin against a group of deserting U.S. soldiers in Laos in 1970. The men allegedly involved were an elite Green Beret A-Team. The report was expressly approved by both CNN Chairman Tom Johnson and CNN President Rick Kaplan. In response, The Pentagon commissioned another report contradicting CNN's. CNN subsequently conducted its own investigation which concluded that the "journalism [in the Valley of Death] was flawed" and retracted the story. In the event, all 12 men of the Green Beret A-Team were wounded in action during Operation Tailwind, which had absolutely nothing to do with sarin.

Three or more of the individuals responsible were fired or forced to resign, for the US Government had insisted that the report was flawed.[11] Arnett was reprimanded.[12]

The co-producers of the report, April Oliver and Jack Smith, were dismissed. They sued Time Warner, the parent company of CNN, claiming they had been wrongfully fired and Time Warner ultimately paid millions of dollars to settle their lawsuits, along with other suits brought by military personnel who claimed to have been libeled in the Oliver/Smith report. Senior producer Pam Hill and others resigned. Oliver was later quoted by the World Socialist Web Site (International Committee of the Fourth International) as saying that:

“

His [Arnett's] firing was a direct result of Pentagon pressure. Perry Smith [a retired USAF major general and former CNN consultant who resigned in protest over the Tailwind report] told the Wall Street Journal last July that CNN would not get cooperation from the Pentagon unless Peter Arnett was fired. [...] They will do anything to stem the flow of information.

Now America is reappraising the battlefield, delaying the war against Iraq, maybe a week and rewriting the war plan. The first plan has failed because of Iraqi resistance. Now they are trying to write another plan ... So our reports about civilian casualties here, about the resistance of the Iraqi forces, are going back to the United States. It helps those who oppose the war when you challenge the policy to develop their arguments.

When Arnett's remarks sparked a "firestorm of protest", NBC initially defended him, saying he had given the interview as a professional courtesy and that his remarks were "analytical in nature". A day later, though, NBC, MSNBC and National Geographic all severed their relationships with Arnett.[14]

In response to Arnett's statement on Iraqi TV, NBC stated:

“

It was wrong for Mr. Arnett to grant an interview with state-controlled Iraqi TV, especially at a time of war and it was wrong for him to discuss his personal observations and opinions.

”

Arnett responded:

“

My stupid misjudgment was to spend fifteen minutes in an impromptu interview with Iraqi television. I said in that interview essentially what we all know about the war, that there have been delays in implementing policy, there have been surprises.

^Arnett, Peter (20 February 1994). "Live from the Battlefield: From Vietnam to Baghdad, 35 years in the World's War Zones". Booknotes. Retrieved 2007-09-12. Elsa Arnett is my daughter. She's 25 years of age, born in Saigon. My wife was a Vietnamese woman. We separated a few years ago, but we're still in touch. Elsa, a bright young lady, and she went to Stuyvesant High School in New York, as an accomplished student, went on to Harvard University. I never had a university education. Well, Elsa compensated for that by going to Harvard University and graduating with high honors and, lo and behold, went into journalism, became a reporter, worked for several months on The Washington Post as an intern and then joined The Boston Globe; spent a couple of years there and, thank goodness, agreed to help me get this book done.

^"Defending John Yoo", TribLIVE (Pittsburgh), 15 March 2009. "Dateline D.C. is written by a Washington-based British journalist and political observer."